US 7106610 B2
A memory interface and a method to interface with high-speed memory devices have been disclosed. One embodiment of the memory interface includes an inductor and a number of transmission lines. The transmission lines are coupled to the inductor in series to couple a number of memory devices to a circuit board.
1. A memory interface comprising:
a resistor coupled to the inductor in series; and
a plurality of transmission lines, coupled to the inductor in series, to couple a plurality of memory devices to a circuit board.
2. The memory interface of
one or more impedance transformers coupled to the inductor in series.
3. The memory interface of
4. The memory interface of
5. A method to interface a circuit board with a plurality of memory devices, the method comprising:
coupling the plurality of memory devices to a semiconductor device by circuitry, the circuitry including an inductor and a resistor coupled to the inductor in series, wherein the circuitry is fabricated on the circuit board and the semiconductor device is a memory controller mounted on the circuit board.
6. The method of
7. The method of
8. The method of
9. A computer system comprising:
a plurality of synchronous dynamic random access memories (SDRAMs);
a memory controller; and
a memory interface coupling the memory controller to the plurality of SDRAMs, the memory interface comprising
a resistor coupled to the inductor in series, and
a plurality of transmission lines coupled to the inductor.
10. The computer system of
11. The computer system of
12. The computer system of
The present invention relates to memory technology, and more particularly, to improving timing and noise margin of high speed memory interfaces.
A double data rate (DDR) synchronous dynamic random access memory (SDRAM) was introduced as a new evolutionary dynamic random access memory (DRAM) to provide a high-performance interface for system memory. As the DDR data rate increases, high-frequency phenomena, such as, channel resonance, inter-symbol interference (ISI), cross-talk, and simultaneous switching noise (SSN), have become critical in determining the performance of memory.
In a typical computer system, memory devices (e.g., SDRAM) are mounted on one or more dual in-line memory module (DIMM). The DIMM is then plugged into a motherboard via a DIMM connector to provide an interface between the memory and the motherboard.
Furthermore, to predict the performance in high-frequency phenomena, and consequently, to improve the memory channel, series of time domain analysis and simulations are performed to design a memory interface. As the memory interface becomes more and more complex, the large amount of time-domain simulation takes a long time to complete. To compete efficiently in the market, the design time of memory interface has to be shortened in order to provide customers with the memory interface sooner.
The present invention will be understood more fully from the detailed description that follows and from the accompanying drawings, which however, should not be taken to limit the appended claims to the specific embodiments shown, but are for explanation and understanding only.
In the following description, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures, and techniques have not been shown in detail in order not to obscure the understanding of this description.
In one embodiment, the inductor 250 has an inductance of 10 nH. In an alternate embodiment, the inductor 250 has an inductance of 8 nH. One should appreciate that inductors of various inductances can be used, depending on a variety of factors, such as, the frequency of operation, the dimensions of the transmission lines, the signal slew rate required, etc. Furthermore, it should be apparent that multiple inductors may be used to practice some embodiments of the present invention instead of a single inductor.
In addition to or as an alternative to using the inductor 250, one may vary the dimension of one or more of the transmission lines 230 to increase the impedance of the memory interface 200. The relationship between the impedance and the dimension of the transmission lines 230 depends on the fabrication process. For example, using an exemplary fabrication process, the impedance of a 7 mil wide transmission line is 50 ohms. The transmission line may be narrowed to 4 mil to provide an impedance of 60 ohms, or be further narrowed to 3.5 mil to provide an impedance of 67 ohms.
In one embodiment, each of the DIMMs 310 includes a number of transmission lines 313 and a structure 315 to provide a certain amount of impedance. In one embodiment, the structure 315 includes an inductor coupled to the transmission lines 313 in series. The structure 315 may further include a resistor coupled to the inductor in series. In addition to or as an alternative to the inductor, the structure 315 may include a single or a multi-section impedance transformer. One should appreciate that each of the DIMMs 310 may have substantially the same configuration. Alternatively, each of the DIMMs 310 may have a distinct configuration depending on the characteristics of the SDRAM devices 340 to which the DIMM 310 is interfacing with.
Processing logic then generates a number of models for various components in a computer chipset, such as, for example, the package, the stackup, and the connector (processing block 430). In one embodiment, processing logic extracts grounding, referencing, and power distribution information from previous memory interface layout design (processing block 440). Using these information, processing logic performs simulation of the models in time domain (processing block 450).
In one embodiment, optimization ranges for the controlled parameters are defined in an Advanced Design System (ADS). In one embodiment, goals are set before running the optimization. Examples of the goals include frequency domain fluctuation, resonance alleviation, smaller return loss and cross talk, etc. In one embodiment, performing the optimization includes simulating at different values of the controlled parameters within the ranges set. Processing logic repeats the optimization in frequency domain until an optimized topology of the memory interface is found (processing block 413).
After optimization, processing logic performs sensitivity analysis to confirm the results from the optimization. In one embodiment, processing logic performs time domain matrix reduction using both the controlled and the uncontrolled parameters 405 (processing block 421). Processing logic repeats the sensitivity analysis in frequency domain until an optimized topology of the memory interface is found (processing block 423). Once the goals set are satisfied, processing logic ends the sensitivity analysis (processing block 425). However, processing logic may change the controlled parameters or the optimization range in response to the sensitivity analysis of a certain parameter if the sensitivity of the parameter is beyond a predetermined level. In addition, the sensitivity analysis may provide information for determining the worst-case stackup matrix for a certain motherboard and DIMM impedance combination. In one embodiment, the sensitivity analysis is based on a Gaussian distribution with 5% or 10% standard deviation.
In one embodiment, the CPU 510, the AGP 530, the DDR DIMMS 525, and the ICH 540 are coupled to the MCH 520. The MCH 520 routes data to and from the DDR DIMMs 525, which are further coupled to a number of DDR SDRAM devices 527. However, one should appreciate that other types of memory, such as, DRAM or flash memory, may be used instead of DDR SDRAM. In one embodiment, each of the DDR DIMMs 525 is mounted on the same motherboard (not shown) via a DIMM connector (not shown) in order to be coupled to the MCH 520. In one embodiment, the USB ports 545, the AC Codec 560, and the switch 550 are coupled to the ICH 540. The switch 550 may be further coupled to a firmware hub 570, a floppy disk drive 551, data input devices 553, such as, a keyboard, a mouse, etc., a number of serial ports 555, and a number of parallel ports 557.
Note that any or all of the components and the associated hardware illustrated in
In one embodiment, the DDR DIMMs 525 include a number of transmission lines and an inductor to provide a certain amount of impedance to reduce the timing slew rate of signals and to increase the signal gain through the DDR DIMMs 525. In one embodiment, the inductor is coupled in series with the transmission lines. In one embodiment, the DDR DIMMs 525 further includes a resistor coupled in series with the inductor. Alternatively, the DDR DIMMs 525 may include a single or multi-section impedance transformer, which may be integrated into one or more of the transmission lines in the DDR DIMMs 525.
Although the technique disclosed is applied to the DDR DIMMs 525 shown in
The foregoing discussion merely describes some exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion, the accompanying drawings and the claims that various modifications can be made without departing from the spirit and scope of the appended claims. The description is thus to be regarded as illustrative instead of limiting.